Environmental pollutants that are known to have harmful effects when introduced into inhabited areas represent a significant health hazard to humans and pets that occupy such areas, because of the acute and/or chronic toxicity caused by exposure to such pollutants. Such pollutants may not be easily controlled at the source, i.e., may be a result of regional air pollution. Certain environmental spaces, such as medical facilities, food storage areas, are particularly susceptible to air pollutants, or biological contamination. Methods for remediating the air and protecting the occupants and contents from exposure to such pollutants and health hazards would therefore be beneficial.
In enclosed spaces, often such methods include passing the air via an air handling system through a fixed solid filter, such as those found on a typical HVAC furnace filter, HEPA filters, or containing an adsorbent material such as charcoal or carbon-black. While this methodology may remove particulate matter, it has limited utility because the filters may become saturated and/or blocked even on short term use. Furthermore this approach is unsatisfactory for the removal of certain other pollutants, including Total Volatile Organic Compounds (TVOC) and gasses, such as formaldehyde (see Clary, John J., et al., “Formaldehyde: Toxicology, Epidemiology, Mechanisms”, First Edition 1983; “Formaldehyde and Other Aldehydes”, Committee on Aldehydes, Board on Toxicology and Environmental Health Hazards, Assembly of Life Scientists, National Research Council, National Academy Press, Washington, D.C. (1981); and “Formaldehyde Health and Safety Guide, IPCS International Programme on Chemical Safety, Health and Safety Guide No. 57). Formaldehyde is a particular problem because it is used widely in furniture and construction. The plywood used, for example may contain a glue resin such as urea-formaldehyde, or phenol formaldehyde resin. In such systems, formaldehyde can gradually release from the resin for as long as 15 years. The formaldehyde vapor often accumulates in an enclosed space as a result. Formaldehyde vapor may also arise from synthetic fibers, plastics, or insulation foam, within or nearby the space. Furthermore, because of the size requirements, the use of traditional air handling units and air purifiers in some enclosed spaces such as small buildings other than homes or offices, trucks, automobiles or motor homes are not practical. Often the only solution has been to ventilate the enclosed space by exchanging its air with outside air, but this solution can necessitate the need to recondition, e.g., cool, reheat, humidify or dehumidify, the air, added to the expense of such a solution. Furthermore, some particles are too small to catch even with HEPA filters. The use of porous porcelain material in filtration systems to catch small particles has been described, but this leads to blockage of the pores and huge energy consumption (and frequent replacement of filter materials). In addition, volatile organic chemicals can get easily saturated on solid media, such as C-black or charcoal, commonly used material for absorbing volatile organic compounds such as formaldehyde. Once saturation of the solid media occurs, it can be released from the solid phase. This is especially true for formaldehyde because of its high volatility (bp of −19° C.), making it readily released from C-black.
For infectious disease-related bacteria or viruses, it is important to not only capture and kill (sterilize or disinfect) the pathogens but also prevent them from growing in the air cleaning process. Removal of harmful microorganisms with such filtration technology is also problematic, because in strong winds or air currents, they can be blown away from solid support (such as charcoal) and released back into the air. Even more problematic, microorganisms may find solid media as ideal environment in for multiplication (growth) before circulating back to the air. The problem is not easily mediated by adding biocides to solid support, because it is inefficient in dry condition or the charcoal may become less absorbent if it is made wet. Furthermore, biocides in solid form may dissociate from the solid support and be released directly into the air, resulting in safety concerns.
A second approach to removing pollutants, such as formaldehyde, from air is referred to as “air washing” and involves systems in which a large quantity of water is recirculated through an airstream. For example, the airflow passing through heating/ventilation ductwork within is subjected to a spray or cascading surface of water, or comes in contact with a water treated media, such as a moistened moving belt, agitated packing material, or frothy interface. The formaldehyde is absorbed into the water, and the formaldehyde/water mixture can be removed and the air washing system can be replenished with fresh formaldehyde-free water. (See Pedersen et al., Environment International, 12, 439-447, 1986; U.S. Pat. No. 6,641,635; US 2004 0028586; U.S. Pat. Nos. 6,669,946, 7,758,025). Similarly, air scrubbing devices are disclosed in which air is passed through a chamber, where a cascade of water circulates, and the water is disinfected by means of a germicidal light source (U.S. Pat. No. 7,722,708) or the scrubbing action is accomplished by means of a central rotor which disperses a liquid through a specially shaped bowl that brings it in contact with passing air (U.S. Pat. No. 3,936,283). Because air washing methods typically result in some of the liquid being entrained in the moving air in droplet form, the addition of an apparatus called an eliminator is employed to remove the droplets. An air washer design with no eliminator is described in U.S. Pat. No. 6,132,493.
A third general approach are various systems designed to remove contaminants such as particulates and/or biodegradable vapors, in which environmental air is pumped below the surface of one or more chambers or compartments containing water and/or another liquid; the water may contain an additive, such as a surfactant, a biologically active microorganism or a biocide which reacts/degrades the contaminants (U.S. Pat. No. 4,818,59; US 2003 0232424; U.S. Pat. Nos. 6,616,733; 5,908,491; 5,078,759; 5,080,793; 5,078,759; 7,022,297; 7,156,895; 7,988,909; 6,626,983; 2,209,775; 5,848,592). This general method of removing pollutants has also been applied to industrial waste streams, where additives are selected to specifically decompose the contaminants. (U.S. Pat. No. 4,251,486). These devices frequently also function as humidifiers, i.e., adding moisture to the air as it is cleaned.
In industrial work areas where environmental hazards are well defined, specialized personal protection equipment have been developed and are routinely used. In contrast, convenient methods to protect individuals from chronic exposure to harmful gasses and particulate matter in public outdoor areas are not readily available, despite deteriorating air quality because of environmental pollution. In some areas of the world, smog has been so severe, that if it contains PM2.5, governments of many countries advise individuals to stay indoors and to keep doors and windows shut to prevent it from entering into houses or vehicles. PM2.5 refers to particulate matter of 2.5 microns or less, and is also referred to as “fine” particles and believed to pose the greatest health risks.
Thus, there is a need for a generally applicable and practical method and devices to remove pollutants, including particulates, volatile contaminants, biological hazards such as germs and viruses from the air of enclosed air spaces and to prevent or reduce exposure of these pollutants to individuals in outdoor environments where needed.